Left in difficulty, lacking sense (5)
I believe the answer is:
blind
'lacking sense' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?
'left in difficulty' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' indicates putting letters inside.
'difficulty' becomes 'bind' (bind is a kind of difficulty).
'l' going inside 'bind' is 'BLIND'.
Can you help me to learn more?
(Other definitions for blind that I've seen before include "Unable to observe" , "Visually challenged" , "cover-up" , "Like a bat" , "without a way out" .)